Amazon calculates a product’s star ratings based on a machine learned model instead of a raw data average. The model takes into account factors including the age of a rating, whether the ratings are from verified purchasers, and factors that establish reviewer trustworthiness.
This APP is probably the best as I keep in contact with family and friends all over USA and Canada. No one phones anymore they just post to FB and everyone is informed of what is going on. My Dad is 92 and he is amazed that I talk to his family in Canada and that they talk back to me. He doesn't understand how it works but he laughs when I show him things on it. It is the greatest.